Calvin Harris has taken to Twitter to defend his decision to axe ex-girlfriend Rita Ora's Teen Choice performance at the weekend

Rita Ora looked glum in London this morning, keeping her head down to avoid being pictured as she relaxed in her comfies.

Looking far from the polished pop star she usually is, the Hot Right Now star looked sullen as she chatted on her mobile phone on the streets, wearing a three-quarter length grey coat over a pair over Adidas tracksuit bottoms and a hoodie.

Rita has not had the best of weeks after she was had to cancel her plans to perform I Will Never Let You Down at the Teen Choice Awards last week.

Talking on the radio with Ryan Seacrest, Rita pointed the finger at her ex-boyfriend Calvin Harris.

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Rita Ora was pictured talking on her mobile phone wearing a grey coat over a similar grey hoodie

"For anybody who doesn't understand how it works, he wrote and produced the song," the singer said.

"So he has to approve anything TV-wise for anybody who doesn't get it. And obviously he owns the rights to it and he didn't approve the Teen Choice Awards."

When it was announced she’d no longer be performing at the Shrine Auditorium in Los Angeles on Sunday, Rita tweeted: . "Guys I am so sorry. I will make it up too you. I promise. I'm devastated. I love my fans.”

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Rita Ora was pictured talking on her mobile phone wearing a grey coat over a similar grey hoodie

Calvin Harris has since defended his decision to block Rita Ora's performance at the Teen Choice Awards on Sunday by going off on one on Twitter about his ex-girlfriend.

It's not the first time one of the singer's ex-fella's has taken to social media to fume about her - but we didn't expect this one coming.

Calvin tweeted: "You'll only know 1 side of the story RE Teen choice awards because I choose not to talk to the papers about every aspect of my personal life (sic)"

Instagram/ritaora

He followed that message up with another tweet insisting his decision to not allow Rita to sing the tune at the Los Angeles ceremony was justified. He wrote: "But just know I had a damn good reason (sic)" WHAT IS IT, CALVIN?!

Calvin, 30, then tweeted an emoticon of a waving hand, appearing to say farewell to his ex and the drama surrounding the decision.

It's not the first time Rita has angered one of her ex-boyfriends leading to them taking to Twitter to hit back at her.

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In 2012, sock entrepreneur Rob Kardashian took to the social networking site to rant about his failed romance with the Hot Right Now hitmaker and alleged she cheated on him with 20 men.

He posted: "She cheated on me with nearly 20 dudes while we were together... But I mean 20?!!!! (sic)"